Two-dimensional tungsten photonic crystal selective emitter: effects of geometrical parameters and temperature

In this paper, we have studied the effects of structural parameters and temperature on the emissivity of a square array of cylindrical nano/microcavities on tungsten slab by finite difference time domain method. It has been shown that the physical nature of the emissivity enhancement depends on the structural parameters of the nano/microcavities. In the case of narrow and shallow nanocavities with radius r <= 150 nm and depth d <= 150 nm; the emissivity has the same behavior as that of flat tungsten. Thermally excited surface plasmon polaritons cause a sharp peak in the emissivity of nanocavities with 150 <= d <= 250 nm and 150 <= r <= 350 nm at wavelength in the order of periodicity, lambda similar to a. In the case of wide and deep microcavities with r = 350 nm and d <= 250 nm; there are anomalous peaks in the emissivity which are well matched with the modified resonant wavelengths of a microcavity. At wavelengths shorter than periodicity, the Bragg diffraction from the surface of periodic microcavities reduces the emissivity. The obtained results show that to have a favorable selective thermal emitter from 2D W nano/microcavities with emission efficiency more than 90%, the periodicity should be as small as possible, the cavity depth should be large enough and its radius should be selected according to the working temperature.